Search

The core/shell material shows novel properties depending upon their relative valance and conduction band shift. In the present work, PbO and PbO/ZnO core/shell nanoparticles are prepared through chemical technique using PVP as capping agent. The core/shell PbO/ZnO exhibits the X-Ray diffraction peaks of both the material, thereby confirming the formation of core/shell structure. The particle size and strain of all the material are calculated employing W.H technique. The UV visible absorption spectra of PbO show a blue shift of its absorption edge. However, after coating with ZnO shell the absorption edge become red shifted. The band gaps were estimated from Taue plots which were found to be reduced from 3.2 eV to 2.74 eV. The reduction of band gap is attributed to the incorporation of defects in terms of shell. The photoluminescence spectra show a band to band emission around 345 nm along with emission from other impurities. After coating the near band gap emission is red shifted towards 374 nm. The PL intensity of the core reduced after shelling. This effect may be attributed to the change of recombination kinetics governed by induced defects.

Journal of alloys and compounds 749, 768 - 775 (2018). doi:10.1016/j.jallcom.2018.03.261, This paper demonstrates fine size-controlled synthesis of superparamagnetic carbon-encapsulated iron nanoparticles, by a supersonic plasma jet assisted rapid, bulk-production process, by manipulation of the pressure in the sample collection chamber. Transmission electron microscopy and small angle x-ray scattering measurements confirmed the formation of single-crystals with a narrow size distribution, having core average size of 5.0 nm and encapsulated by an ultrathin carbon coating, for sub-mbar pressure. VSM and Mossbauer characterization established the nanocrystallites to be superparamagnetic in nature, with saturation magnetization 67 emu/g and coercive field 7.4 Oe. Controlled plasma heating during synthesis led to the burning down of extra carbon that resulted in further enhancement of the magnetization of the product. Graphitization of the encapsulating layers also enhanced, which could successfully protect the metallic core from oxidation, as well as improved its cyto-compatibility. This purified sample could be ideal for targeted drugs delivery and water treatment applications. Another sample was processed through controlled reaction with oxygen, the as-synthesized sample having magnetic properties approaching that of the first sample, which may be more attractive especially for water treatment processes because of the simpler single-step processing of the material., Published by ScienceDirect, Amsterdam [u.a.]

In this communication, we identify some thermal-plasma assisted synthesis techniques for the alternative production of fusion relevant tungsten dust particles in bulk amounts, to allow for the statistically meaningful study of their hydrogen absorption properties. Fast, single step synthesis of fine particles in the α-tungsten phase was demonstrated, using a high heat flux device for sizes in the micrometer region and an experimental nanoparticle reactor for dust with nanometer sizes. Production of both equilibrium polyhedral and nonequilibrium spherulitic crystal shapes was demonstrated, dust morphologies similar to which were identified before in existing tokamaks and divertor simulator systems. Their hydrogen retention characteristics were measured by the Nuclear Resonance Reaction Analysis technique, which was found to be orders of magnitude higher compared to the same metal in the bulk form. The mesoporous crystals generated during high power, high pressure synthesis conditions were assumed to be responsible for the unusually high gas retention of the nanoparticle sample. It was concluded that non-equilibrium tungsten dust morphologies would be dominant in the high power fusion machines in the future, which may aggravate the hydrogen isotope retention issues further.

This article reports the synthesis of tungsten nanoparticles predominantly in α-W phase by a single step plasma expansion technique. The oxidation of the metal and contribution from the β-W phase in the nanomaterial samples was observed to decrease with the increase of both the pressure in the sample collection chamber and the plasma power. We had observed production of faceted, lightly sintered particles with up to 300 nm individual sizes during high plasma current/high pressure synthesis conditions, which were measured to have the highest specific surface area of 35 m 2 /g. Condensation of this high temperature material at low saturation ratio and the high collisional regime had led to the synthesis of relatively bigger particle sizes in this experiment. Cauliflower like particle morphologies was observed during low pressure synthesis conditions, which is considered to have formed through spherulitic growth processes. Transmission Electron Microscopy (TEM) micrographs show very small crystallites remaining dispersed in an amorphous moss like the background, which was confirmed to be a mixture of tungsten and its oxides.

This paper reports rapid, continuous and carbon-nanotube free synthesis of carbon encapsulated magnetic nanoparticles by thermal-plasma expansion technique, which combines the typical advantages of high-temperature plasma assisted synthesis method with efficient particle-size control. Core nanocrystals were encapsulated with few layers of graphitized carbon, which could provide protection against both oxidation and intense chemical treatment. The average iron/iron-carbide nanoparticle diameter (7.7, 9 and 10 nm) and the width of the size distribution increased with pressure in the sample collection chamber, as a result of the decreasing quenching rate of the plasma jet. This also resulted in the smaller particles remaining frozen predominantly in the high-temperature γ-Fe phases, part of which was oxidized subsequently and eliminated preferentially during the purification process. All samples could be correlated with smooth variation of magnetic properties; saturation magnetization, remnant magnetization and coercive-field enhancing with increasing chamber pressure or average particle size. The low pressure synthesized sample with smallest average particle size approached super-paramagnetic behavior (saturation magnetization = 51.8 emu/g, ratio of remnant to saturation magnetization = 4.9 and coercive field = 52 Oe), which may be ideal for biomedical applications. High-pressure samples on the other hand have a higher saturation magnetization (76.3 emu/g) and coercive fields (123 Oe).

Nanoparticles of crystalline, phase-pure γ-alumina is synthesized in a supersonically expanded thermal plasma jet assisted experimental chemical reactor, with good control over the average particle sizes independently with respect to plasma current, oxygen flow rate and the ambient pressure in the sample collection chamber. Most of the synthesized particle samples were seen to be transparent, which gets more transparent with decrease in the particle sizes. The lowest achievable pressure in the chamber had produced particles with average 10 nm sizes, which was best also in terms of narrow size distribution. Another important observation was the absence of serious inter-particle agglomeration, producing free-flowing particles. Optical emission spectroscopic technique was used to study the plasma chemistry of the reaction zone as well as the plasma jet.

This paper reports controlled synthesis of carbon nanoparticles by an expanded thermal plasma jet assisted technique through a single-step, high-throughput process. The plasma discharge zone in the experimental reactor remained isolated from the particle nucleation/growth chamber through a supersonic nozzle, which allowed using the sample collection chamber pressure as an efficient control parameter to synthesize carbon nanostructures with tailored combination of some important properties. Low chamber pressure conditions produced samples with both good specific surface area and crystallinity, which may be ideal for use as an efficient catalyst support material as well as in batteries and super capacitors. This dominantly mesoporous sample was also found to have good hydrogen absorption properties. Another significant observation was that the average number of carbon nano-sheets stacked together inside the crumpled paper like layers increased with pressure in the sample collection chamber. Optical emission spectroscopic techniques were used to measure the effective cooling rates responsible for the particle nucleation process under different experimental conditions, which also indicated that C2 dimer molecules are the basic precursors behind the formation of these carbon nanostructures.